Constructing embankments, such as dike embankments, roads and highways, airport runways and railroads, involves depositing layers of soil on the existing ground. Due to the weight of the deposited soil the existing ground tends to subside. Said subsiding may amount to several meters. To compensate for this subsiding additional soil has to be deposited until a stationary state is reached. Upon completion of settlement the construction of the embankment can be completed and finished. Monitoring means are required to determine if settlement has been reached. For some structures, the monitoring may continue during the lifetime of the embankment such as airport runways which need to be continuously monitored for stability and flatness or dikes for structural integrity. The monitoring means should be capable to measure this with a resolution and accuracy of a few cm. For this purpose solutions are known based on measurement of a pressure of a hydraulic liquid as determined by an electrical pressure transducer buried in the deposited soil or in the existing ground near their interface. A reservoir with the hydraulic liquid is located away from the construction and a liquid-filled tubing runs from the reservoir down to the embedded pressure transducer. The transducer measures the pressure created by the column of liquid in the tubing and issues a signal to a readout module. The pressure of the liquid is indicative for the height of the column and therewith for the extent to which the existing ground is subsided due to the deposited soil.
In practice it does not suffice to monitor the settlement at a single position only. Typically it is necessary to monitor the settlement, for example every 50 m, over the entire length of the embankment, which may be considerable. The length may for example amount to various kilometers. Furthermore, in many situations several points along the width are desired to be monitored, further increasing the number of measurement points needed. Monitoring the settlement with the known solution therefor is costly as it requires a large number of sensor units each comprising a pressure transducer, tubing, reservoir and readout unit.
Accordingly there is a need for embankment monitoring means that is more cost effective.